ABC has ordered an extra episode of the procedural dramedy, TVGuide.com has learned. The addition will bring the Season 5 total to 24 episodes.The extra hour will air in April, replacing a previously scheduled repeat episode. Castle, which stars Nathan Fillion and Stana Katic as crime-solving partners-turned-lovers, is averaging 9.9 million viewers a week and scoring a 1.98 among the adults-18-to-49 demographic.